1. Field of the Invention
The present invention relates to a chuck provided on a machine tool for supporting shafts, hollow cylinders, or other rotationally symmetrical components.
2. Description of the Prior Art
A chuck of this kind is disclosed in DE 195 02 363 C1. In this chuck, a hole extending in the longitudinal direction of the chuck body is provided in one end of the chuck body, and an actuation piston is inserted therein so as to be axially movable. The actuation piston drives three wedge rods via intermediate elements. The wedge rods being mounted in holding pockets disposed in the chuck body and adapted to be moved axially therein. The wedge rods are provided with helical gearing which interacts with one clamping jaw each in a driving connection. Furthermore, three guide grooves extending radially are disposed in the free end of the chuck body, and one of the clamping jaws is adapted to be inserted into the guide groove. As soon as the clamping jaw is in a positive-locking active connection with the corresponding wedge rod via its helical gearing, the wedge rod can be moved via the actuation piston, and the helical gearing between the wedge rod and the underside of the clamping jaw causes the corresponding clamping jaw to be advanced radially in the direction of a workpiece to be clamped.
Chucks of this kind have proven effective in practice and are used in a large number of machine tools. When clamped workpieces are machined, contamination arises, for example, due to the cooling lubricants used, or as a result of metal chips separated from the workpiece. This contamination in the form of liquid particles, metal chips, and the like, is deposited in the guide grooves running in the direction of the workpiece, as a result of which increased friction occurs between the clamping jaw and the guide groove, or the wedge rod, as it advances. This causes the clamping force to be reduced, as a result of which reliable securing of the workpiece to be machined is no longer guaranteed. The guide grooves can be manually cleaned to remove the contamination, but this is time-consuming and thus costly.
This problem has been recognised, and in EP 1 759 793 B1 a chuck is described in which a lubricant supply is provided for each of the three guide grooves. The driving active connection between the clamping jaw and a clamping or actuation piston is effected using a wedge hook coupling according to this state-of-the-art.
It is a disadvantage in the operation of this chuck that has been disclosed that the lubricant emerges from the guide grooves due to the centrifugal forces in the direction of pockets in which counterweights are arranged. The pumps built into the pockets are intended to pump the lubricant collected in the pockets in the direction of the guide grooves. In this state-of-the-art, there is no permanent separate lubrication of the guide groove during the advance movement of the clamping jaws.
The guide grooves mean that contamination not only gets between the grooves and the clamping jaws, but in particular, also onto the wedge rods when these are actuated. It is a disadvantage that the wedge rods are not protected against contamination in the chuck body, and that lubricant exclusively enters between the clamping jaw and its guide grooves, and not at the wedge rod, or at least not in such a way that the helical gearing of the wedge rod and the clamping jaws is cleaned, or such that the contamination enters between the wedge rod and the inner wall of the chuck body and solidifies there, as a result of which the wedge rod has to be actuated against increased friction resistance. However, this reduces the clamping forces and leads to wear on the wedge rod, or the chuck body, as a result of which there are inaccuracies in clamping the workpieces.